Incremental Forming (IF) is a flexible sheet metal forming technique that uses tooling to locally deform sheet metal along a predefined toolpath to impart the sheet with a desired or designated shape, such as a three-dimensional shape. Single Point Incremental Forming (SPIF) uses one tool on one side of the sheet to cause the deformation. One drawback with SPIF is an inherent geometric inaccuracy of creating the designated shape due to unintended non-local deformation and subsequent springback of the sheet in the single point setup.
One potential solution to the unintended non-local deformation in SPIF is to use partially cut out blanks along a periphery of a forming area in the sheet. While the obtained geometric accuracy of the sheet may be improved over SPIF described above, this technique of using the partially cut out blanks may not useful in improving geometric accuracy in IF relative to the significantly better geometric accuracy provided by use of a partial support of the sheet, in spite of the resultant loss in process flexibility associated with using such a support. A closed-loop feedback control has been used in some known SPIF processes to improve the geometric accuracy in SPIF by forming the component in a second iteration. Although the result obtained from the second iteration was better than the initial iteration, such a process may be time consuming and difficult to be implemented for freeform objects, such as asymmetrical objects, objects whose shape is not defined by a single mathematical relationship (e.g., equation or function between two or more geometric axes), amorphous objects, and the like.
Other variations of IF include die-based IF (DBIF), which uses a die below the sheet, and double-sided IF (DSIF), which uses one tool above the sheet and another tool below the sheet. One drawback to DBIF is that the process can be limited to forming components on one side of the sheet only and can require process planning that is specific to the part geometry being formed. For example, the die that lies below the sheet may need to be separately formed in advance of the forming of the sheet. This additional processing step and equipment adds to the cost and complexity of the forming of the sheet.
In DSIF, two tools can be located on either side of a sheet, with each tool mounted on a robot that controls movement of the tool. The tools may be moved toward each other to squeeze the sheet between the tools and to form desired shapes. For example, the gap between tools may be smaller than the thickness of the sheet to form a “squeezing toolpath” of the tools. This technique, however, may require an accurate thickness prediction of the sheet because, if the thickness prediction is inaccurate, one or more of the tools may lose contact with the sheet and DSIF will degenerate to SPIF. To maintain contacts of both tools with the sheet, a forming tool that is displacement controlled (e.g., the tool is controlled to move designated distances independent of the force imparted by the tool on the sheet) and a supporting tool that uses both displacement control (as previously described) and force control (e.g., the tool is controlled to exert a designated force on the sheet, independent of the distance that the tool is displaced to impart the force) may be used. While this technique could provide contact between the supporting tool and the sheet, the amount of force to be applied to the sheet and a preset angular offset for the supporting tool may need to be determined through time-consuming, repetitive trials or experiments each time the shape of the completed component (to which the sheet is formed) changes. Furthermore, depending on the global shape of the component, the force required to form the shape may change.
In the known DSIF techniques described above, conventional “out-to-in” toolpaths were used for the forming tool. In such a toolpath, the forming begins with the tool disposed at or near the outermost periphery of the sheet or component to be formed (e.g., where the component is formed from less than all of the sheet, a location at or near the outer edge of the final, completed component) and travels all the way down to the actual component depth, while moving in the X-Y plane of the sheet. For example, the tool may move from the outer edge of the component toward the center of the component. Such a toolpath may require the controls (e.g., displacement control for the top tool and both displacement and force control for the bottom tool) described above.